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The Supplement Research Compendium
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Lactobacillus casei Shirota

Lacticaseibacillus paracasei Shirota (Yakult)

The original Yakult strain — best evidence for preventing antibiotic-associated diarrhoea and supporting bowel regularity

Moderate evidence 🦠Probiotics🛡️Gut & Immune

✚ Updated · How we grade evidence

Evidence tier
Moderate
Research weight
Citations
9 verified / 9
Classification
Probiotics
❝
What the evidence says. Several controlled trials; effects real but modest or context-dependent.

What is Lactobacillus casei Shirota?

Lactobacillus casei Shirota (Lacticaseibacillus paracasei Shirota (Yakult)) is a probiotic strain used for reduces antibiotic-associated diarrhoea and c. difficile-associated diarrhoea in hospitalised older adults (hickson 2007). NutriDex grades the human evidence as Moderate. Lacticaseibacillus paracasei (formerly Lactobacillus casei) strain Shirota, the live culture in Yakult, is one of the most studied probiotic strains, almost always delivered as a fermented-milk drink rather than a capsule. Its best-supported use is preventing antibiotic-associated diarrhoea (AAD): the landmark Hickson 2007 BMJ trial cut AAD from 34% to 12% and C. difficile diarrhoea from 17% to 0% in hospitalised older adults, though a later rigorous spinal-cord-injury RCT (ECLISP) found no overall AAD benefit except in proton-pump-inhibitor users. Randomised trials also show modest, reproducible improvement in stool consistency and defecation frequency, reduced winter upper-respiratory-tract infections in office workers, and blunting of stress-related cortisol rise and abdominal symptoms in exam-stressed students. Effects are strain- and dose-specific and tend to be modest; results across indications are mixed rather than uniformly positive.

Purported Benefits

✓Reduces antibiotic-associated diarrhoea and C. difficile-associated diarrhoea in hospitalised older adults (Hickson 2007)
✓Lowers AAD risk in antibiotic-treated patients who regularly take proton-pump inhibitors (ECLISP subgroup)
✓Improves stool consistency and increases defecation frequency in people prone to constipation or with soft stools
✓Reduces the incidence and duration of winter upper-respiratory-tract infections in healthy adults
✓Blunts stress-induced salivary cortisol rise and relieves stress-associated abdominal symptoms under academic stress
✓May modestly improve metabolic markers (post-meal glucose handling) in obese pre-diabetic adults

Evidence by outcome

The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.

OutcomeEvidenceEffectStudies
Reduces antibiotic-associated and C. difficile diarrheaHickson 2007 strongly positive, but the rigorous ECLISP RCT found no overall AAD benefit. Mixed ↔ mixed · moderate 2
Lowers AAD risk in regular proton-pump-inhibitor usersECLISP subgroup only (28% vs 53%); post-hoc subgroup, hypothesis-generating. Preliminary ↑ benefit · moderate 1
Improves stool consistency / defecation frequencySingle crossover RCT in adults with soft stools; modest, strongest in constipation-prone subjects. Preliminary ↑ benefit · small 1
Reduces winter upper-respiratory-tract infections in healthy adultsOne office-worker RCT (22% vs 53%); single fermented-milk trial, not replicated here. Preliminary ↑ benefit · moderate 1
Blunts stress-induced cortisol rise / stress abdominal symptomsTwo RCTs in exam-stressed students; small samples, gut-brain surrogate endpoints. Preliminary ↑ benefit · small 2
Improves metabolic/post-meal glucose markersOne RCT in obese pre-diabetic men showed only modest metabolic changes. Preliminary ↔ mixed · small 1

Dosing & Compounds

Typical Dose
Typically 6.5 x 10^9 to 1 x 10^11 (about 6.5 billion to 100 billion) live LcS cells once daily, taken as a fermented-milk drink. For AAD prevention, given once daily during the antibiotic course and continued ~7 days after; for regularity, respiratory and stress outcomes, daily intake over 4-12 weeks.
Active Compounds
Yakult / Yakult Light fermented-milk drink (~6.5-10 billion LcS per 65 mL bottle)Yakult 1000 / Y1000 (~100 billion LcS, marketed for stress and sleep)Strain designations: Lacticaseibacillus paracasei Shirota, L. casei strain Shirota (LcS), YIT 9029Almost exclusively a probiotic fermented-milk beverage rather than a capsule or powder

Safety & Cautions

Generally well tolerated; trials report no serious intervention-related adverse events, and a surveillance study in critically ill children found no LcS colonisation or bacteraemia. As with all live probiotics, use caution in critically ill, severely immunocompromised, or central-venous-catheter patients, in whom rare lactobacillus bacteraemia/endocarditis has been reported with the genus. The drink contains milk and added sugar (relevant for lactose intolerance and diabetes/glycaemic control). Probiotics do not replace standard treatment for active infection. Educational only — always check with your doctor or pharmacist before combining Lactobacillus casei Shirota with any medicine.

Key Studies

RCT (subgroup analysis) Wong 2024 (ECLISP subgroup) ✓ PubMed
In the proton-pump-inhibitor subgroup, LcS lowered AAD incidence at 30 days vs placebo (28.0% vs 53.3%; p=0.01), suggesting benefit restricted to regular PPI users.
RCT Wong 2021 (ECLISP) ✓ Full text
Multicentre double-blind RCT in spinal-cord-injury patients found a single-strain LcS drink did NOT prevent AAD overall, with no significant difference in AAD incidence vs placebo.
RCT Shida 2017 ✓ Full text
In healthy middle-aged office workers, daily LcS-fermented milk over winter significantly reduced the incidence of upper-respiratory-tract infections (22.4% vs 53.2%; p=0.002) and shortened their duration.
RCT Kato-Kataoka 2016 ✓ PubMed
In medical students under exam stress (n=24 per arm), 8 weeks of LcS-fermented milk preserved gut-microbiota diversity and significantly suppressed stress-induced abdominal dysfunction vs placebo.
RCT (pooled) + animal Takada 2016 ✓ Source
Pooled human RCT data showed LcS suppressed the pre-examination rise in salivary cortisol and reduced physical (abdominal/cold) symptoms, modulating the gut-brain axis.
RCT Hibberd 2019 ✓ PubMed
In obese pre-diabetic Japanese men, a randomised double-blind placebo-controlled trial of LcS-fermented milk assessed effects on metabolic abnormalities, showing modest changes in glucose/metabolic markers.
RCT (crossover) Sakai 2011 ✓ PubMed
In healthy adults with soft stools, 4 weeks of LcS-fermented milk significantly hardened stool consistency vs placebo and normalised defecation frequency, with effects strongest in those tending toward constipation.
RCT Hickson 2007 ✓ PubMed
In 135 hospitalised older patients on antibiotics, LcS drink reduced antibiotic-associated diarrhoea from 34% to 12% (absolute risk reduction 22%; 95% CI 7-37%) and C. difficile diarrhoea from 17% to 0%.
Safety/surveillance study Srinivasan 2006 ✓ PubMed
Bacteriologic surveillance in critically ill children found no LcS colonisation or bacteraemia and good tolerability, supporting the strain's safety profile.
9 sources cited · 9 verified Search all studies on PubMed ↗

Common questions about Lactobacillus casei Shirota

What is Lactobacillus casei Shirota used for?

Lactobacillus casei Shirota is most often taken for Reduces antibiotic-associated diarrhoea and C. difficile-associated diarrhoea in hospitalised older adults (Hickson 2007), Lowers AAD risk in antibiotic-treated patients who regularly take proton-pump inhibitors (ECLISP subgroup), Improves stool consistency and increases defecation frequency in people prone to constipation or with soft stools, Reduces the incidence and duration of winter upper-respiratory-tract infections in healthy adults. The original Yakult strain — best evidence for preventing antibiotic-associated diarrhoea and supporting bowel regularity

Does Lactobacillus casei Shirota work — what does the evidence say?

Moderate evidence. Several controlled trials; effects real but modest or context-dependent. Lacticaseibacillus paracasei (formerly Lactobacillus casei) strain Shirota, the live culture in Yakult, is one of the most studied probiotic strains, almost always delivered as a fermented-milk drink rather than a capsule. Its best-supported use is preventing antibiotic-associated diarrhoea (AAD): the landmark Hickson 2007 BMJ trial cut AAD from 34% to 12% and C. difficile diarrhoea from 17% to 0% in hospitalised older adults, though a later rigorous spinal-cord-injury RCT (ECLISP) found no overall AAD benefit except in proton-pump-inhibitor users. Randomised trials also show modest, reproducible improvement in stool consistency and defecation frequency, reduced winter upper-respiratory-tract infections in office workers, and blunting of stress-related cortisol rise and abdominal symptoms in exam-stressed students. Effects are strain- and dose-specific and tend to be modest; results across indications are mixed rather than uniformly positive.

What is the typical dose of Lactobacillus casei Shirota?

Typically 6.5 x 10^9 to 1 x 10^11 (about 6.5 billion to 100 billion) live LcS cells once daily, taken as a fermented-milk drink. For AAD prevention, given once daily during the antibiotic course and continued ~7 days after; for regularity, respiratory and stress outcomes, daily intake over 4-12 weeks.

Is Lactobacillus casei Shirota safe? Any cautions or side effects?

Generally well tolerated; trials report no serious intervention-related adverse events, and a surveillance study in critically ill children found no LcS colonisation or bacteraemia. As with all live probiotics, use caution in critically ill, severely immunocompromised, or central-venous-catheter patients, in whom rare lactobacillus bacteraemia/endocarditis has been reported with the genus. The drink contains milk and added sugar (relevant for lactose intolerance and diabetes/glycaemic control). Probiotics do not replace standard treatment for active infection.

How many studies support Lactobacillus casei Shirota?

NutriDex cites 9 sources for Lactobacillus casei Shirota, graded "Moderate".

Cite this page
APA

Peh, D. (2026). Lactobacillus casei Shirota (Lacticaseibacillus paracasei Shirota (Yakult)): Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 26 Jun 2026, from https://nutridex.info/s/l-casei-shirota

BibTeX
@misc{nutridex_l_casei_shirota,
  author       = {Peh, Daryl},
  title        = {Lactobacillus casei Shirota (Lacticaseibacillus paracasei Shirota (Yakult)): Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/l-casei-shirota},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-06-26}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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